Paper machine roll bearings: arrangement, lubrication and failures
A paper roll is a huge steel tube on two bearings. It runs continuously, often for years between stops. Every position in the machine has its own bearing logic because the loads, temperatures and speeds are so different.
Typical duty
| Speed | Load | Temperature | Typical life |
|---|---|---|---|
| Up to about 100 rpm to 1,000 rpm by section | Heavy radial from roll mass and nip load | Dryer journals hot, up to 100 °C and more | 120,000 – 200,000 h design targets |
How the bearings are arranged
Press or dryer roll · one fixed, one floating
Used when: Press, felt and drying cylinders
A roll sits on two bearings at its ends. A roll warms and grows in length, and the frame has some bending, so the two bearings cannot both be locked. One is locked. The other must allow the shaft to move and tilt, and a toroidal roller bearing (CARB) does this better than any other type.
Common failures and how to prevent them
| Failure | What you see | Why it happens | Prevention |
|---|---|---|---|
| Inner ring cracking from thermal stress Thermal cracking | Axial crack through the inner ring, usually at start-up of a dryer. | Inner ring cooler than the journal, which stretches the ring until it cracks. | Choose C4 clearance and a case-hardened HA3 ring, and warm the roll up slowly. |
| Water in the oil Moisture corrosion | Milky oil, corrosion pits. | Steam, wash water or a failed seal. | Keep seal purge air on, check oil regularly for water, and fix leaks early. |
| Misalignment and roll deflection Misalignment & distorted seats (edge loading) | Off-centre wear and rising temperatures at one bearing. | Roll bends under load, or housings are not aligned. | Use the toroidal or spherical type that suits the deflection, and align on a warm machine. |
| Standstill marks False brinelling | Marks at roller spacing after shutdowns. | Vibration from neighbouring rolls while the roll is stopped. | Turn rolls slowly during long stops. |
| Contaminated oil Abrasive wear | Dull, scratched raceways. | Poor filtration, fibre or filler particles in the oil. | Filter the oil and replace it on analysis, not just on time. |
| High bearing temperature Overheating & lubricant breakdown | Discoloured rings, burnt oil. | Heat from the roll journal and too little oil flow. | Insulate the journal and check oil flow rate and temperature. |
Lubrication
Circulating oil
Standard on press, suction and dryer rolls. Gives cooling, filtration and long life.
Viscosity
Chosen from speed and temperature, usually a high-viscosity mineral or synthetic oil. Follow the roll maker.
Oil analysis
Water and particle count tell you what the bearings are experiencing long before noise or temperature changes.
Sealing
- Labyrinth with air purge: Non-contact seals that stay tight as the roll expands. Purge air stops steam and spray entering.
- Contact seals: V-rings or lip seals on slower rolls, with regular inspection.
What to watch
- Bearing temperature per roll, with trend and alarms.
- Oil analysis for water and particles.
- Vibration on suction and press rolls, which see the highest relative bearing speed.
- Axial movement at the floating end after hot running.
Questions
Which bearings are used in paper machine rolls?
Press or dryer roll · one fixed, one floating: Press, felt and drying cylinders.
What are the common bearing failures in paper machine rolls?
Inner ring cracking from thermal stress: Inner ring cooler than the journal, which stretches the ring until it cracks. Water in the oil: Steam, wash water or a failed seal. Misalignment and roll deflection: Roll bends under load, or housings are not aligned.
How should paper machine rolls bearings be lubricated?
Circulating oil: Standard on press, suction and dryer rolls. Gives cooling, filtration and long life. Viscosity: Chosen from speed and temperature, usually a high-viscosity mineral or synthetic oil. Follow the roll maker.